The present invention relates to agricultural ground-engaging tools; and more particularly, to an automatic spring reset shank for a ground-working tool, such as a fertilizer applicator unit.
There have been attempts to provide fertilizer shanks with automatic reset features using springs to apply an initial preset force resisting any movement of the shank from the field working position. The preset force is generated through a predetermined preload on the reset spring. Once the preset force is overcome, such as when the shank encounters a bolder or other rigid object, the shank pivots upwardly and rearwardly in an effort to clear the obstruction. The reset spring compresses, applying an increased reset force. Eventually, however, the reset force reaches a maximum as the shank rises; and further displacement of the shank creates a reduced reset force, thereby facilitating clearance of the object. This characteristic is known in the art and is referred to as a parabolic force curve. Upward displacement of the shank is commonly referred to as tripping. The horizontal force required to induce tripping is referred to as the trip force.
One such attempt at providing an automatic reset force having a parabolic force/displacement characteristic is described in U.S. Pat. No. 4,463,813. The design in the ""813 patent, however, has a number of structural characteristics upon which the present invention improves. For example, in the ""813 patent, the depth of the shank is controlled through adjustment of a spring tension bolt, in an effort to alleviate unnecessary stress on the mount when the shank is in the working position. Moreover, the design of the ""813 patent uses intricate, expensive castings to mount and compress the reset spring. Furthermore, the maximum trip position of the shank in the ""813 patent is controlled by means of a spring compression casting. The casting includes a stop member which extends from the main pivot of the shank. In addition, the reset spring of the prior art design is oriented approximately 20xc2x0 beneath the horizontal and extends downwardly and rearwardly relative to the main spring pivot which is mounted to a bracket mounted on the main transverse frame member to which the shank assembly is mounted.
The present invention includes a shank pivot weldment which carries the shank and knife assembly, and is pivotally mounted to a mount weldment. The mount weldment is releasably mounted to a toolbar or transverse frame member of the implement carrying the tools. The present invention is disclosed in the context of a fertilizer applicator, but persons skilled in the art will appreciate that the automatic reset feature on the present invention is applicable to other ground-working agricultural tools.
The mount weldment includes an upright guide plate which is mounted flush with the rear vertical surface of the toolbar, and includes a lower slot, opening downwardly, to receive the shank pivot weldment. A plate attached to the mount side plates spanning the distance between side plates located upward and forward of the lower spring mount provides additional strength to the weldment and slot defines the raised or tripped position of the shank assembly by limiting the motion of the shank pivot weldment in the maximum raised position. The lower position of the shank assembly is defined by a saddle carried by side plates of the mount weldment.
The shank assembly is biased to the lowered or field working position by means of a spring assembly. One end of the spring assembly is pivotally mounted to the rear of the shank pivot weldment, and the action line of the spring extends upwardly and rearwardly at about 65xc2x0 above the horizontal from that lower pivot point of the spring assembly. An upper spring bracket of inverted U-shape mounts the top of the reset spring to the mount weldment and provides an upper spring pivot axis located approximately midway of the length of the spring and intersecting the action line of the spring.
The spring is pre-loaded to provide an initial holding force of approximately 1,000 lbs., and the design of the elements is such that the vertical clearance of the shank is approximately 8 inches.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of the preferred embodiment accompanied by the attached drawing, wherein identical reference will refer to like part in the various views.